Already known are laser beam machines, in which an impeller rotatable at high speed is arranged between an optical component forming a light path and a workpiece to be machined, to prevent contaminants such as sputters, oil mist, etc. produced during machining from adhering to optical components of the laser beam machine.
A principal part of a conventional laser beam machine of this type provided with an impeller rotatable at high speed is schematically shown in the sectional side elevation of FIG. 7. In the figure, a laser beam emitted from a laser oscillator is reflected at a mirror 2 in a machining head 1 toward a parabolic mirror 3 and then focused by the parabolic mirror 3 to irradiate a workpiece 4 to be machined. Also, an assist gas is introduced into the machining head 1 from supply means, not shown, through a pipe 5, and then supplied to the workpiece 4 after being throttled by a nozzle 6 mounted to a distal end of the machining head 1, thereby melting the workpiece 4 for machining by the interaction of the laser beam and the assist gas.
An impeller is arranged between the parabolic mirror 3, which is the endmost optical component for the laser beam emission, and the workpiece 4. The impeller 7 comprises a rotary shaft 9 to be rotated at high speed by a motor M as rotating means, and a plurality of vanes 10 attached radially to the rotary shaft 9, and repels contaminants 8 scattering from the surface of the workpiece 4, thereby preventing the contaminants 8 from adhering to the parabolic mirror 3. That is, the impeller 7 functions as a contaminant repellent member.
The impeller 7 is rotated by the motor M at such a high speed that the contaminants 8 scattering from the surface of the workpiece 4 during machining are struck by at least one vane 10 without fail while they pass through the rotating vanes 10 from below. The scattering contaminants 8 are thus surely repelled by the vanes 10, whereby the contaminants 8 are prevented from reaching the parabolic mirror 3.
In the conventional laser beam machine, however, rotation of the impeller 7 is controlled by means of general-purpose commands which are independent commands designed for ON/OFF control of external equipment; therefore, rotation of the impeller 7 cannot be controlled unless such commands are specified in a machining program.
The following is an example of a machining program for a conventional laser beam machine equipped with the impeller 7:
______________________________________ Line No. Statement ______________________________________ 1. L P[1] 100 mm/sec FINE 2. DO[1] = ON 3. LASER START 4. L P[2] 100 mm/sec CONT 100 5. L P[3] 100 mm/sec FINE 6. LASER END 7. DO[1] = OFF 8. [END] ______________________________________
In the above program, the statements of Line No. 1, 4 and 5 are declarations for commanding movements to target positions P[1], P[2] and P[3] which have respectively been defined in advance in the machining program, moving speeds, interpolation types and the like. The statement of Line No. 3 is a declaration for commanding a pre-flow (preliminary emission of the assist gas) and the start of emission of the laser beam. The statement of Line No. 6 is a declaration for commanding the end of emission of the laser beam and an after-flow (continued emission of the assist gas for a predetermined time), and the statement of Line No. 8 is a declaration for commanding the end of the program. The statements of Line No. 2 and 7 are independent general-purpose commands used for ON/OFF control of external equipment; in the above example, the commands are used for ON/OFF control of the motor M which controls the rotation of the impeller 7.
As long as contaminants 8 scatter from the workpiece during a laser beam machining, the motor M must be driven to rotate the impeller 7, and therefore "DO[1]=ON" must be defined before the statement "LASER START". Further, at a stage in the program where a laser beam machining for a specific part is ended or the entire machining program ends, "DO[1]=OFF" must be defined to stop the rotation of the impeller 7. Setting of these statements for ON/OFF control is left entirely to an operator who prepares the machining program. Thus, if the operator forgets setting the rotation start command "DO[1]=ON", laser beam machining is carried out with the impeller 7 stopped, thereby causing the fear of having the contaminants 8 adhere to the parabolic mirror 3. Even though the rotation start command is set at a proper location, contaminants 8 will not be fully repelled if laser beam machining is started before the rotational speed of the impeller 7 reaches a predetermined speed, possibly contaminating the parabolic mirror 3. Further, if the statements for ON/OFF control are frequently used in cases where laser beam machining is started after it is ascertained that the rotational speed of the impeller 7 has reached the predetermined speed, loss of time associated with increase of the rotational speed is accumulated, prolonging the overall machining time.